The present invention relates to magnetic recording and reproducing apparatuses having devices for tracking control of rotary magnetic heads. More particularly, the invention relates to a magnetic recording and reproducing apparatus having a device which performs tracking control by controlling the positions of the rotary magnetic heads so as to correct for tracking deviations of the rotary magnetic heads which inevitably occur particularly during still-picture reproduction, slow-motion reproduction, and quick-motion reproduction thereby to obtain accurate and positive tracking of the rotary heads.
The assignee of the present invention has previously developed a system wherein tracks are formed on a tape without gaps to guard bands between adjacent tracks. Moreover, a color video signal can be recorded and reproduced on such a tape without the occurrence of an interference beat disturbance. This system is described in U.S. patent application Ser. No. 731,935, now U.S. Pat. No. 4,178,606, entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, and assigned to the assignee of this application. In this previously developed system, a pair of azimuth heads have gaps which are inclined with a certain azimuth angle, in mutually opposite directions with respect to a direction perpendicular to the longitudinal direction which is of the track. Adjacent tracks are formed in contiguous contact side-by-side without a gap or guard band therebetween. The phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period. The direction of this phase shifting is reversed from one track to the next adjacent track. In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other. Moreover, there is no beat disturbance.
On the other hand, the prior art employs a system wherein a video signal is recorded on a magnetic tape in parallel tracks, formed obliquely to the longitudinal direction of the magnetic tape. This tape may either be stopped or transported at different speeds at the time of playback in order to carry out a speed-change in the reproduction, such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this known system, the tape travel speed at the time of reproduction is different from that at the time of recording. The tracing path of the rotary head relative to the tape during reproduction differs from the tracing path (track) of the rotary head during recording, whereby so-called tracking deviation occurs.
In the proposed system mentioned above, when tracking deviation occurs as a result of reproduction at changed speed, a so-called reverse tracking, in which one of the heads traces a part of a track recorded by a head having the same azimuth as the other hand, occurs partially. With respect to this part traced by reverse tracking, there is almost no reproduction of the recorded signal because of azimuth loss. For this reason, when tracking deviation occurs, the reproduced signal level drops, and, in accordance with this, a noise component due to a reduction of the reproduced signal level accompanying tracking deviation will appear at irregular positions on the reproduced picture screen. For this reason, the noise part in the picture moves, and the S/N ratio of the entire picture becomes poor. Consequently, a speed-change reproduced picture cannot be obtained in good picture quality.
Accordingly, as a system for correcting for tracking deviation at the time of changed-speed reproduction, a control system in which displacement devices in which piezoelectric elements are used are separately provided respectively for a pair of rotary magnetic heads on a rotary structure, and the magnetic heads are separately caused to undergo displacement by their respective displacement devices, whereby each rotary head accurately carries out correct tracking, has been devised.
However, since it is necessary in this devised control system to provide displacement devices separately for respective rotary magnetic heads, the composition of the system becomes complicated. Furthermore, in the case where there is a deviant difference between the operations of the rotary magnetic heads, both rotary magnetic heads cannot be satisfactorily tracking controlled in a mutually interrelated manner.